An ex vivo biomechanical study of equine neonatal rib fracture repair by different fixation methods

Rib fractures result in significant morbidity and mortality of equine neonates. Various methods to repair these fractures have been described but biomechanical testing in immature equine neonatal bone has not been performed. The study objective was to compare strength, stiffness, and mode of failure for four different methods of equine neonatal rib fracture repair.

Ribs were randomly allocated to one of four repair groups: nylon cable tie (NCT), modified reconstruction plate (MRP), string of pearls plate (SOP), or rib clip (RC). Ribs were fractured under three-point bending to induce a simple, transverse fracture. The fracture was reduced and repaired according to the assigned repair group, then tested to failure under single-cycle four-point bending. Strength (maximum force, F_max, and force at failure, F_fail) and mode of failure were recorded. Stiffness (N/mm²) was calculated. Data was analyzed using linear mixed models.

In intact ribs, no significant differences in F_max (p = 0.46), F_fail (p = 0.35), or stiffness (p = 0.90) were observed between groups. Among repair groups, F_max, F_fail, and stiffness differed significantly (p < 0.0001). NCT repairs had significantly lower F_max and F_fail than MRP and SOP, while MRP and SOP had greater stiffness compared to NCT and RC. NCT and RC groups failed at the original fracture site, whereas MRP and SOP failed mostly due to screw pullout.

Rigid fixation with MRP or SOP provides stronger fracture repair than NCT or RC when equine neonatal ribs are tested under single-cycle load to failure. Further investigation of both rigid and non-rigid repair methods with cyclic loading is warranted.